Turbofan gas turbine engines for powering aircraft conventionally comprise a core engine, which drives a fan. The fan comprises a number of radially extending fan blades mounted on a fan rotor which is enclosed by a generally cylindrical, or frustoconical, fan casing. The core engine comprises one or more turbines, each one of which comprises a number of radially extending turbine blades enclosed by a cylindrical, or frustoconical, turbine casing.
There is a remote possibility with such engines that part, or all, of a fan blade, or a turbine blade, could become detached from the remainder of the fan or turbine. In the case of a fan blade becoming detached this may occur as the result of, for example, the turbofan gas turbine engine ingesting a bird or other foreign object.
The use of containment rings for turbofan gas turbine engine casings is well known.
In the event that a blade becomes detached, the casing is subjected to two significant impacts. The first impact occurs generally in the plane of the rotor blade assembly as a result of the release of the radially outer portion of the rotor blade. The second impact occurs downstream of the plane of the rotor blade assembly as a result of the radially inner portion of the rotor blade being projected in a downstream direction by the following rotor blade.
Our published European patent application EP1245791A2, published 2 Oct. 2002, describes a fan blade containment assembly to reduce damage and/or penetration of the fan casing downstream of the plane of rotor blade assembly.
Our published UK patent application GB2281941A, published 22 Mar. 1995, describes a fan blade containment assembly comprising three layers. The first layer comprises a fan casing adjacent the fan blades, the second layer comprises a plurality of deformable tubes arranged with their axes arranged parallel to the axis of the gas turbine engine and around the fan casing and the third layer comprises a strong woven fibrous material around the deformable tubes.